This invention relates generally to a display apparatus which includes a display panel, a video driver and a timing generator. The invention relates specifically to a driving control technique for a display apparatus which adopts a plural pixel simultaneous sampling system, and more specifically to a technique for removing noise included in a video signal to be supplied from a video driver to a display panel.
A plural pixel simultaneous sampling system is effective as a driving system for a display panel represented by a liquid crystal display panel of the active matrix type and is disclosed, for example, in Japanese Patent Laid-Open No. Hei 4-116687. According to the plural pixel simultaneous driving system, a color display panel includes a plurality of signal lines which are disposed in parallel to each other in a vertical direction. Each successive three signal lines make up a set for the colors of red (R), green (G) and blue (B). Further, the color display panel includes a plurality of gate lines arranged in parallel to each other in a horizontal direction. Furthermore, the color display panel includes pixel electrodes individually connected to intersecting points of the signal lines and the gate lines via respective switching elements. The pixel electrodes are arranged at a predetermined arrangement pitch in a matrix. In addition, the color display panel includes a plurality of horizontal switches individually provided corresponding to the signal lines. Further, the color display panel includes three video lines connected for the individual colors to the signal lines via the horizontal switches and accepts video signals of R, G and B supplied thereto from a video driver. In the plural pixel simultaneous sampling system of the construction described above, a horizontal driving circuit for simultaneously controlling the horizontal switches in units of a set for the colors R, G and B and performs RGB three pixel simultaneous sampling driving. In this instance, a sample and hold unit is provided in the video driver for relatively providing delay amounts corresponding to the arrangement pitch of the pixels to the video signals of R, G and B supplied to the three video lines. By relatively providing the delay amounts corresponding to the arrangement pitch of the pixels to the video signals of R, G and B and controlling opening and closing operations of the horizontal switches simultaneously in units of a set for R, G and B, the number of stages of horizontal driving circuits (for example, shift registers) for driving the horizontal switches is reduced to achieve simplification in construction and also to reduce the power dissipation while a good color display image is obtained. Since the horizontal switches for R, G and B are constructed so that the opening and closing operations thereof are simultaneously controlled by a selection pulse outputted from a shift register, the number of stages of the shift registers is reduced to one third. Further, also the frequency of a horizontal clock signal to be supplied from a timing generator is reduced to one third.
In a display apparatus which adopts the plural pixel simultaneous sampling system, video signals to be inputted to a display panel of the active matrix type are produced by a video driver built in a sample and hold unit. However, an ordinary sample and hold unit produces, at timings at which the on-off operation is changed over alternately, noise originating from sample and hold leakage. Since the noise is supplied in a superposed condition on the video signals to the display panel, the display apparatus has a problem to be solved in that a display defect in the form of a vertical stripe appears on the screen and deteriorates the picture quality remarkably.